In recent years, gas supply facilities equipped with a so-called “pressure type flow controller” to be employed for a gas supply facility to a process chamber have been widely used with semiconductor manufacturing facilities and the like.
FIG. 8 illustrates one example. It is so constituted that pressure type flow controllers C1, C2 and C3 and fluid switching valves D1, D2 and D3 are provided, and switching of the fluid supplied to the process chamber E, and flow rate adjustments, are automatically performed with signals from a controller B (TOKU-KAI-HEI No. 11-212653 and others). Also, it is so constituted that, with the afore-mentioned pressure type flow controllers C1, C2 and C3, a flow rate passing through an orifice is computed by a computation device M, using the formula Qc=KP1, by maintaining the fluid passing through an orifice Ka under critical conditions (i.e., P1/P2 larger than approximately 2) as illustrated in FIG. 9. The computed flow rate is used to control opening or closing of a control valve V0 (to adjust pressure P1 on the upstream side of an orifice) so that a difference Qy with a set flow rate Qs is made to be zero. Here, A/D designates a signal converter and AP designates an amplifier (TOKU-KAI-HEI No. 8-338546).
As illustrated in FIG. 10, the internal pressure of the afore-mentioned process chamber E is maintained at a set value (10−6˜102 Torr) by continuously operating a vacuum pump VP through an evacuation line Ex having a comparatively large bore equipped with an automatic pressure controller APC and a conductance valve CV.
A combination of a primary vacuum pump (a high vacuum pump) VP1, such as a turbo molecular pump and the like, and a secondary vacuum pump (a low vacuum pump) VP2, such as a scroll pump and the like, is commonly used for the afore-mentioned vacuum pump VP. However, this exhaust system, for which one vacuum pump having a large exhaust volume and large compression ratio is used, has disadvantageously high manufacturing costs and the like, so it is not popular. An internal pressure of chamber E is maintained solely by the operation control on the exhaust system side. Specifically, a set internal pressure is maintained by adjusting the degree of opening of the automatic pressure controller APC and conductance valve CV.
However, with a process chamber E, as shown in FIG. 10, continuous operation of the primary vacuum pump VP1 and the like, such as a turbo molecular pump having a high compression ratio and a large exhaust volume, is required. Furthermore, to reduce loads on the primary vacuum pump VP1 and the secondary vacuum pump VP2, it becomes necessary that the diameter of the pipe for the evacuation system Ex needs to be relatively large. In addition, a conductance valve CV, an automatic pressure controller APC, and the like, are required. Accordingly, equipment costs and operating costs of running the vacuum chamber E are high, so it is difficult to achieve reduction of costs with this system.
With a process chamber E, as shown in FIG. 10, internal pressure of the chamber is controlled using only the operation control of the automatic pressure controller APC and the like. This results in problems such as a low operating rate of the process chamber, which leads to unevenness in quality of treated products because too much time is needed for adjusting the internal pressure of the chamber due to so-called “poor pressure control responsivity.”
On the other hand, to raise responsivity of internal pressure of the chamber E, measures to control the flow rate of gas supplied into the chamber E might be taken in addition to the control of the exhaust side. However, it is necessary to substantially improve accuracy of the flow rate of gas supplied into chamber E so, over a wide range of pressures, the internal pressure of chamber E may be adjusted by adjusting the flow rate of gas into the chamber E.
A fluid supply facility connected to chamber E, as shown in FIG. 8, has the feature that pressure type flow controllers C1, C2, C3 used in the facility are not influenced by internal pressure changes on the side of chamber E. Therefore, a comparatively stable control of the flow rate of the supply gas is ensured as long as critical conditions are maintained, thus achieving an excellent, practical effect.
However, various difficulties with this type of fluid supply facility have been found. Among those difficulties, there is a particular need to raise accuracy of flow rate control in the small flow quantity range (i.e., small gas flow rates). For example, assuming that the accuracy of flow rate control of a pressure type flow controller, which has a rated flow rate of 1 SLM (“Standard liter/min:” a flow rate of a gas converted to a standard state), is 1% F.S. (“Full Scale”) less than a setting 10%. In this case, there is a possible maximum error of 1 SCCM (“Standard Converted cm3/min”) when the value of the control flow rate is set at 1% of the rated flow rate. Accordingly, when the control flow rate becomes less than 10% of the rated flow rate (for example, less than 10-100 SCCM), The effect of the error of the afore-mentioned 1 SCCM is no longer negligible and cannot be ignored. As a result, accurate flow rate control cannot be expected in the small flow quantity range, which is less than 100 SCCM.
Patent LiteratureTOKU-KAI-HEI No. 11-212653Public BulletinPatent LiteratureTOKU-KAI-HEI No. 8-338546Public Bulletin